feat(reader): 🎉 Add support for multi-file DBML loading

* Implement directory reading for DBML files.
* Merge schemas and tables from multiple files.
* Add tests for multi-file loading and merging behavior.
* Enhance file discovery and sorting logic.

pkg/writers/dbml/writer.go

@@ -126,7 +126,15 @@ func (w *Writer) tableToDBML(t *models.Table) string {
 			attrs = append(attrs, "increment")
 		}
 		if column.Default != nil {
-			attrs = append(attrs, fmt.Sprintf("default: `%v`", column.Default))
+			// Check if default value contains backticks (DBML expressions like `now()`)
+			defaultStr := fmt.Sprintf("%v", column.Default)
+			if strings.HasPrefix(defaultStr, "`") && strings.HasSuffix(defaultStr, "`") {
+				// Already an expression with backticks, use as-is
+				attrs = append(attrs, fmt.Sprintf("default: %s", defaultStr))
+			} else {
+				// Regular value, wrap in single quotes
+				attrs = append(attrs, fmt.Sprintf("default: '%v'", column.Default))
+			}
 		}
 
 		if len(attrs) > 0 {